Multiple studies indicated that the degree of muscle strain is the most relevant parameter in understanding the injury mechanism behind a hamstring strain injury. To monitor this parameter a new system is developed; the Smart Sensor Shorts. The system contains five Inertial Measurement Units (IMUs) integrated in a sports tights. The purpose of this study was to develop a methodology to estimate the muscle strain and muscle elongation velocity of the biceps femoris (BF), semimembranosus (SM) and the semitendinosus (ST) muscle in professional and recreational football athletes with the use of IMUs during different football specific movements and during different intensities. When comparing different movements and intensities, the greatest peak muscle strain was found in the BF and the lowest peak muscle strain was found in the SM during the majority of the movements. The biomechanical load was different for each hamstring muscle and was different for the running based movements and other football specific movements. The BF experienced the greatest peak muscle strain (12.12 ± 0.88%) during a maximal intensity kick in the supporting leg, while the greatest peak muscle elongation velocity was observed in the ST (3.97 ± 0.47 s-1) in the kicking leg during the maximal intensity kick. The greatest biomechanical loading was during a maximal intensity kick. Finally, it was observed that the moment of peak muscle strain was different from the time period of peak muscle elongation velocity for running based movements. It is concluded that IMUs together with the developed methodology could be used in the assessment of hamstring strain injuries in professional and recreational football by analyzing and monitoring muscle strain and muscle elongation velocity.

This exploration study focuses on the braking behaviour of World Tour cyclists during a descent. For this study, 8 riders descended over 6 trials using a ‘sensor bike’. As part of this particular study, a novel brake sensor is developed and validated in practice. The sensor package can be transferred between bicycles, allowing each rider to use his own bicycle. Results of the exploration study indicate that for the chosen descent, braking and cornering skills are not decisive for overall time over the descent. However, significant time differences are found for the corner which is analysed. Time difference reported over this corner are approximately one second. With a shortest cornering time of 10.14 seconds this is a significant difference. The brake behaviour of theWorld Tour cyclists could be split into two distinct braking strategies: • ’stop brake late’ ( where braking is stopped late and well into the turn). • ’stop brake early’ (where braking is stopped before or early in the turn). It was found in this study that the best brake strategy is ’stop brake late’. The peak brake forces measured during the descent are much lower than the maximum brake forces reported in literature. This implies, that performance can still be improved by increasing brake forces at the first part of the braking action, so the braking can start later. The results found in this study can contribute to optimise braking and cornering skills of riders by explaining and showing where improvements can be found. An additional result is that the brake sensor revealed unexpected brake rub at certain parts of the descent, especially when riders are accelerating. Eliminating this brake rub, can improve rider performance. The riders also shows clear signs of learning behaviour as can be observed in the obtained data. For future research it is recommended to add a speed sensor to the sensor package. Recommended small improvements for the brake sensor are identified. Using this improved sensor package, trials could be rehearsed on a steeper descent, such that pedalling actions have less influence, exploring braking and cornering strategies further.

On all levels of rowing, a general rule is that you have to row together. Rowing together has no clear-cut definition. However, it is known that each rower has his or her own style, which can be registered in movement patterns and force curves. The big question is how to combine these individual styles such that the crew works together in the best way. The Dutch Rowing Federation showed interest in this topic, wanting to know how to adjust the rigging dimensions of the boat to allow the best racing performance. The goal of this thesis is to provide advice on what features of the rowing stroke should be synchronized and whether and how this could be promoted by individualized rigging.

The theoretical foundation for this study was a literature study about the current knowledge on the rowing stroke and differences within and between individuals and crews. Current used measures on performance and synchronization of rowers were described, and finally a proposal was done for which methods to use in the ongoing of the study.

Data was obtained from five female athletes of elite level, doing trials in a quadruple sculls of approximately 30 seconds at 30 SPM and 32 SPM in four different combinations. The strokes were identified and analyzed, based on performance and synchronization measures. Performance measured as Average Speed, Work per Stroke, Blade Losses, Velocity Fluctuation Losses and their respective and combined efficiencies. Synchronization measures were defined as Mean Standard Deviation of the Phase, Standard Deviation of the Time to Half Impulse and Standard Deviation of the Time to Half Work.

The chosen synchronization measures were not completely independent. Standard deviations of time to half impulse and half work were found to be highly similar (r = 0.970). An opposite effect was found between kinematic synchronization and the other two, Mean Standard deviation of the Phase was not in line with the empirical rule that better synchronization leads to better performance. The kinetic and energetic measures did show this effect: Lower standard deviations of time to half impulse and time to half work meant higher average speed (r = −0.193) and higher Work per Stroke (r = −0.574).

The best performing synchronization measure was time to half impulse synchrony. A drawback on this measure was that the sampling period was long, compared to the interpolated time differences. Athletes were found to achieve their half impulse moments in a consistent order.

To find out whether it is possible to promote synchronization and thus performance by individualizing rigging, the oar angles at the time to half impulse were analyzed. This new measure correlated moderately (r = 0.624), meaning it quantifies more or less the same effect. The kinetic similarity actually worked better (r = −0.292 with Average Speed and r = −0.748 with Work per Stroke) than the synchronization measure.

Similarity of half impulse angles enables the coach to adjust the rigging such that the timing should improve too. However, this should be tested in a follow-up study.